The Gamer's Graphics & Display Settings Guide

[Page 7] Graphics Settings - Refresh Rate



Refresh Rate


Refresh Rate is not to be confused with Frames Per Second. FPS is how fast your graphics card can output individual frames each second; Refresh rate is a separate property of a CRT computer monitor: how many times per second it can 'refresh' the screen, regardless of how many frames are being fed to it by the graphics card, or what type of image is on the screen. Most of this section applies only to CRT monitors, however if you own an LCD monitor, read through this section because as you will come to see, most of it does actually wind up applying to LCD panels for reasons which are explained in the Response Time section.


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A traditional CRT computer monitor works in much the same way as your TV set, and both have similar internals: a glass picture tube covered in phosphors, and an electron gun sitting at the back. To create an image, the electron gun moves and shoots a beam at the phosphors on the front of the tube, briefly lighting them up with an image. It starts at the top left corner of the screen and rapidly 'paints' the screen line by line, across and down the face of the tube. Once it hits the bottom, the electron gun turns off, goes all the way back to the top left corner and starts again. This pause between refreshes is called the Vertical Blanking Interval. A monitor refreshes itself incredibly fast many times a second, so that even though at any one point in time much of the screen may actually be blank, waiting to be redrawn by the electron gun, your eyes - due to Persistence of Vision - still see the previous image that was displayed there a fraction of a second ago.


Refresh rate is measured in frequency (Hz) which translates into the number of times per second your monitor actually redraws the entire screen. Thus a refresh rate of 60Hz means that your monitor will actually redraw the entire screen contents 60 consecutive times during a single second; 85Hz is 85 times, and so forth. This is fairly straightforward, but remember, this is how fast your monitor is refreshing the image on the screen with the electron beam, not how many FPS your system is actually producing or displaying. Let's examine the difference.


FPS vs. Refresh Rate


As previously mentioned, FPS and refresh rate are two separate things. Even if the image on your screen has not changed in any way (e.g. a still 2D image like your Windows Desktop), or your 3D game isn't actually supplying enough new frames (e.g. the game is running at 25 FPS on a 60Hz refresh rate), the screen is still being redrawn a fixed number of times based on the current refresh rate of the monitor; if your FPS is less than your refresh rate at any time, some frames may simply be redrawn several times by the monitor.


However if your FPS is higher than your refresh rate at any time, your monitor will not actually be able to display all of these frames, and some will come out with a graphical glitch known as Tearing. To prevent this, you can enable an option called Vertical Synchronization (VSync). However here's the tricky part: if VSync is enabled, then your refresh rate and FPS will actually have a relationship to each other - they will become synchronized together, and your FPS may even fall a great deal overall. This is all covered in more detail in the Vertical Synchronization section.


Screen Flickering


Since a CRT refresh actually involves rapidly lighting up an otherwise black screen, if there are too few refreshes in a second your eyes will become acutely aware of the subtle gaps or changes between refreshes as a form of flickering. This is why all CRT monitors support a minimum refresh rate of 60Hz, as this is thought to be the absolute minimum rate at which most people do not notice significant flickering. Movie projectors use duplicate shutter movement, and TVs use the Interlace method to also raise their refresh/flicker rate to at least 60 or more actual refreshes, even though their source material stays at 24 and 30 FPS respectively.


By themselves, frames don't go blank in between each new frame. The old one stays displayed until the new one comes along to replace it. So while low framerate is certainly annoying and feels terrible, it's not as bad for your eyes. What causes visible flickering is the constant refreshing of the screen on a CRT, that constant change in brightness. Thus a low refresh rate is bad since it's similar to someone blinking a torch into your eyes, or flicking the light switch on and off in your room many times a second.


The notion of a 'minimum acceptable refresh rate' has a lot to do with how fast various creatures are designed to take in a continuous stream of information through the eyes. Animals which are designed to move faster than us, like birds of prey, can typically take in much more visual information and hence would notice flickering even at 80Hz refresh rates for example. Humans on the other hand may not notice obvious flickering at 60Hz or above, but as we discuss in the Frames Per Second section, the human eye has been tested and shown to be able to detect the contents of even 1 frame in every 200 per second. So even if you consciously don't notice the flickering from a CRT running at a low refresh rate, it can still cause problems such as headaches, eye strain and even nausea due to the subconscious impact.


Refresh rates also differ for each Resolution and by screen size on CRTs, and this can have an impact on flicker. In general the higher the resolution being used on a CRT, the lower the maximum refresh rate possible at that resolution. This makes sense, since the electron gun refreshing the screen can only move so fast - if you give it more information to redraw, it does it relatively less quickly. And the larger the surface area of the screen you are looking it, the higher the refresh rate needs to be to prevent obvious flickering. Which is why 60Hz may have been sufficient when we used 15" screens, but is no longer sufficient for the 17", 19" or even larger screens common today. So what is an optimal refresh rate?


Recommended Refresh Rates


All of this discussion leads to me to highlight some basic recommendations about refresh rates. However, because the human eye is involved, these are guidelines only. Each person is different in their tolerances and so you may notice flickering at a much higher or much lower refresh rate than another person. Note once more, none of this discussion relating to flickering applies to LCD monitors, as they don't flicker - see the Response Time section.


Firstly, to check your monitor's maximum supported refresh rates at each resolution you will need its user manual, or search for the model number on the Internet and find its specifications.


Next, to actually set Windows XP to use the highest possible refresh rate supported by your monitor at every resolution, you should first install your monitor's drivers, either from a disk that came with your monitor or through the manufacturer's website. Then use a small utility called Refresh Force, which is the recommended method. It is quite straightforward to use and does everything automatically. It can also provide you with a list of your maximum supported refresh rates at each resolution once you click the 'Auto Populate' button. Alternatively you can use the Refresh Override functions in your graphics card's control panel. For details of all these methods, see the bottom of this page of my ATI Catalyst Tweak Guide or this page of my Nvidia Forceware Tweak Guide as relevant. Do not manually assign higher refresh rates than those in your monitor specifications or detected by utilities like Refresh Force - doing so will give an 'Out of Frequency' error and also may cause damage to the monitor. Monitors cannot refresh faster than the maximum rate specified for each resolution, this is a hardware limitation and cannot be forced any higher.


The absolute minimum supported refresh rate for all monitors should be 60Hz, but this is not optimal. This is the default rate which Windows XP forces for every resolution, and unfortunately most people will notice flickering and discomfort at 60Hz. Studies now place the minimum acceptable refresh rate at around 70-72Hz, and this is the recommended minimum refresh rate at all resolutions. This is generally acceptable on a 19" monitor and should result in little to no noticeable flickering for the majority of people. For resolutions which you will spend a great deal of time looking at, like your Windows Desktop, I strongly recommend an 85Hz or even 100Hz refresh rate, especially if you have a larger screen size. This will help to greatly reduce eye strain in the long run.


The problem is that some CRT monitors do not support high refresh rates, particularly at the higher resolutions at which people game (1280x1024 or 1600x1200 in particular). If your CRT monitor does not support 70Hz (or preferably 85Hz) or more at the resolutions you commonly use, or you still notice flickering, or get headaches or eye fatigue after a period of time playing at certain resolutions, then you need to either lower your resolution to one with a higher refresh rate; consider buying a new CRT monitor with higher refresh rate capabilities; or switch to an LCD monitor which does not flicker at any resolution or size. Do not sacrifice the long term health of your eyes over the cost of a monitor upgrade.